1. Field of the Invention
The present invention generally relates to shipping containers, and more specifically to a shipping container having sidewalls that can be rotated from a horizontal, stowed position, which minimizes storage and transportation costs of empty containers, to a vertical position allowing containers to be loaded and stacked two or more containers high.
2. General Background of the Invention
For many years, industries dealing in bulk goods have utilized returnable containers featuring folding sidewalls that minimize the cost associated with storing and transporting empty containers. In general, such containers include a first pair of opposing sidewalls (“primary sidewalls”) that must be the first two walls raised to an upright position. Such primary sidewalls typically have edge portions that wrap around toward the other primary sidewall. Such containers also generally contain a second pair of opposing sidewalls (“secondary sidewalls”) that can be raised to an upright position only after the primary sidewalls have been raised to their upright position. The edge portions of the secondary sidewalls will typically engage the “wrap around” edge portions of the primary sidewall to add rigidity to the container. Frequently, the edge portions of the primary sidewall and the secondary sidewall are designed to mate together, for example by providing recesses in the edge portion of the primary sidewalls to receive protuberances extending from the edge portions of the secondary sidewalls.
In many applications, such configurations provide the necessary strength and resiliency. But when loaded containers are transported while stacked, problems can arise when the bottom container is brought to an abrupt stop. This results in the momentum of the upper container applying an outward force to the sidewall of the lower container that is facing the direction in which it had previously been moving. Such containers are generally able to withstand such force when applied to one of the secondary sidewalls, especially when the edge portions of the primary and secondary sidewalls are design to mate together so long as the length of the wrap around portion of the primary sidewalls is kept to a minimum to minimize the moment applied to the primary sidewalls.
When such an outward force is applied to one of the primary sidewalls, failures occur on a much more frequent basis. The reason for this is that the latching mechanism and the mating of the sides through recesses and fingers do not collectively have the strength to resist a large outward force applied to the upper portion of the primary sidewall. The primary means of trying to overcome this is by extending the length of the wrap around edge portions of the primary sidewalls to make the primary sidewall more rigid. This, however, has the effect of increasing the moment resulting from an outward force applied to a secondary sidewall and leads to more failures resulting from the application of this type of force. Extending the wrap around edge portion also has the drawback of reducing the width available for a drop-down access panel or door in the secondary sidewall (such drop-down panels are frequently provided to facilitate access to goods stored within such containers).
What is needed then is a container with folding sidewalls that is capable of resisting the outward force applied to any one of its sidewalls resulting when a stack of loaded containers is being moved and the bottom container is brought to an abrupt stop. Such container should also be capable of passing the standard industry inclined impact test that involves placing two loaded containers (the load for each container can be as much as 2000 pounds) with one container stacked on the other. The loaded containers are then allowed to slide down an inclined surface, and at the terminal point of the test the bottom container is impacted and brought to an abrupt halt, resulting in the momentum of the upper container placing an outward force on the upper portion of the downhill sidewall of the bottom container.